This proposal outlines studies designed to determine the role of endogenous non-cyclooxygenase metabolites of arachidonic acid in the modulation of the response of renal mesangial cells to growth factors and peptide vasoconstrictors. Inhibitors of the metabolism of arachidonate via cytochrome P450 monooxygenase and possibly lipoxygenase pathways potently suppress mitogenesis in mesangial cells. Mechanisms of this effect are unclear. One potential site of modulation is the calcium signal. The same inhibitors which suppress mitogenesis also markedly reduce the calcium transient following stimulation with peptide vasoconstrictors without affecting inositol polyphosphate release. Other data suggest an alteration in both the inositol trisphosphate-induced release of calcium from intracellular stores and an effect on cell membrane calcium channel function. It is postulated that non-cyclooxygenase eicosanoids modulate the intracellular expression of inositol polyphosphates, Ca++, and other messengers which couple mitogen-cell interactions to cell proliferation. The first specific aim will be to determine the mechanism of this modulation of the calcium transient. Effects on intracellular release as well as calcium channel function will be determined. The second specific aim will be to determine how these eicosanoids interact with signal transduction pathways other than the calcium messenger system. Specifically, these studies will determine whether they modulate protein kinase C activity, the tyrosine phosphorylation of growth factor receptors, or a novel protein tyrosine phosphorylation pattern recently identified here in mesangial cells in response to mitogenic vasoconstrictors. These studies should help clarify the function of non-cyclooxygenase metabolites of arachidonate in modulating growth.